Arlington CountyArlington CountyArlington CountyArlington CountyStorm Sewer Capacity StudyStorm Sewer Capacity Study

July 30, 2013

Department of Environmental Services,Office of Sustainability and Environmental

Management

Original streamnetwork

50+ miles of

Storm

50+ miles of natural streams

drainage network

332 miles of storm drain pipesdrain pipes38 miles of

streams

June 25, 2006 stormJune 25, 2006 stormJune 25, 2006 stormJune 25, 2006 storm• 350+ calls

reporting stormreporting storm and sanitary sewer issues

• June 2006 storm peak intensity 4.8 in/hrJ 2006• June 2006 storm volume 5 4 in5.4 in

Storm Sewer Capacity Storm Sewer Capacity Analysis GoalsAnalysis Goals

• Reduce potential stormwater threats to ppublic health, safety, and property

• Develop system models that can provide d f d ha roadmap for upgrades to the system

• Ability to prioritize proposed storm sewer t dsystem upgrades

• Comply with State and Federal stormwater and floodplain managementstormwater and floodplain management regulations

Modeling ApproachModeling ApproachModeling ApproachModeling Approach

• 36” diameter pipes and larger

• Surveyed stream cross sections

• Utilize existing plans for pipe diameters, length, inverts

• Pilot study modeled 11 storm distributions

• Analysis model 2 storms• June 2006 storm from Donaldson Run

gagegage• 10yr-24hr SCS Type II storm

Capacity Analysis Scope

• 7 Watersheds•Crossman Run•Westover Branch•Little Pimmit Run•Lubber RunLubber Run•Doctor’s Branch•Spout Run•Roaches

M d l d 36% f th l d• Modeled 36% of the land area to be modeled• Modeled 45% of pipes 36” diameter and larger to be gmodeled• Majority of the June 2006 calls are from these watershedswatersheds

Crossman RunCrossman Run

• 230 Acres

• 44% Impervious, mainlyresidential land use

5 800 LF Pi M d l d• 5,800 LF Pipe Modeled

• 22% of the storm sewer system

• 1,200 LF Pipe to be Upsized

• 21% of the modeled system

• 4 Potential Projects for upsizing

• Entire system is pipedy p p

Doctor’s BranchDoctor’s Branch

• 890 Acres

• 43% Impervious, mainly residentialland use

• 30,500 LF Pipe & 4,100 LF StreamModeled

• 30% of the storm sewer system• 30% of the storm sewer system

• 13,800 LF Pipe to be Upsized

• 45% of the modeled system

• 20 Potential Projects for upsizing

Little Little PimmitPimmit RunRun• 970 Acres

• 37% Impervious, mainly residential land useresidential land use

• 20,900 LF Pipe & 3,700 LF Stream Modeled

• 20% of the storm sewer system

• 11,300 LF Pipe to be Upsized

54% f th d l d t• 54% of the modeled system

• 17 Potential Projectsfor upsizingp g

• 1 Project currently indesign

Lubber RunLubber Run• 1,030 Acres

• 46% Impervious mainly• 46% Impervious, mainlyresidential land use

• 35,200 LF Pipe & 5,500 LFStream Modeled

• 29% of the storm sewer system

• 18,600 LF Pipe to be Upsized

• 53% of the modeled system

• 21 Potential Projects forupsizing

Roaches RunRoaches Run• 625 Acres

• 67% Impervious,mainly commercialmainly commercialuse

• 29,300 LF Pipemodeled

• 26% of the stormsewer systemsewer system

• 11,500 LF Pipe to beupsized

• 39% of the modeledsystem

• 10 Potential Projectsfor upsizing

Spout RunSpout Run • 1,070 Acres

• 50% Impervious

• 41,500 LF Pipe &41,500 LF Pipe &3,500 LF Streammodeled

25% f th t• 25% of the stormsewer system

• 26,000 LF Pipe to be, pupsized

• 63% of the modeledsystemsystem

• 28 Potential Projectsfor upsizing

Westover BranchWestover Branch• 300 Acres

• 38% Impervious, mainlyid ti l l dresidential land use

• 8,000 LF Pipe Modeled

• 23% of the storm sewer system

• 6,400 LF Pipe to be Upsized

• 80% of the modeled system

• 8 Potential Projects for upsizing

• Entire system is piped

• Project at Lee Hwy/John MarshallProject at Lee Hwy/John Marshallessentially complete.

Capacity Analysis Results

Watershed LF Modeled Pipe to be upsized

% Modeled Pipe to be upsized

Planning level cost estimate ($1000)be upsized to be upsized estimate ($1000)

Crossman Run 1,200 21 700Doctor’s Branch 13,800 45 7,500Little Pimmit Run 11,300 54 5,400Lubber Run 18,600 53 8,400Roaches Run 11,500 39 6,700oac es u ,500 39 6, 00Spout Run 26,000 63 17,900Westover Branch 6,400 80 4,500T t l 88 800 52 51 100Total 88,800 52 51,100

• Based on the 10yr-24hr SCS Type II Storm• John Marshall Drive at Lee Hwy in Crossman Run already completed• John Marshall Drive at Lee Hwy in Crossman Run already completed• Little Pimmit Run has already had several projects completed to reduce flooding• 111 Potential Projects (The 8 High Priority projects already identified in the CIP)

Potential Storm Sewer UpsizingPotential Storm Sewer Upsizingp gp g

L h ll iLess challenging projects

• Minimal existing utilities

• Existing pipes within Ri ht f WRight-of-Way

• Minimal property owners to coordinate on construction impacts

• Larger roadway width for installationinstallation

Potential Storm Sewer UpsizingPotential Storm Sewer Upsizingp gp gMore challenging projectsprojects

• Many existing utilities –sanitary watersanitary, water

• Existing parallel pipe systems already in place

• Pipes on private property require easements and agreement from all propertyagreement from all property owners to be completed

• Small roadway width for i i t ll tipipe installation

Next StepsNext Stepspp

• Prioritize Projects (on the County website)

http://www.arlingtonva.us/departments/EnvironmentalServices/Sustainability/page89756.aspx

• Incorporate projects into the SW Master Plan and CIPIncorporate projects into the SW Master Plan and CIP

• Coordinate with other County projects in theimmediate vicinity: stormwater retrofits sanitary sewerimmediate vicinity: stormwater retrofits, sanitary sewerimprovements, water mains, etc.

Questions?Questions?Questions?Questions?

Allan RowleyAllan RowleyDepartment of Environmental ServicesOffice of Sustainability and Environmental ManagementStormwater Infrastructure Grouparowley@arlingtonva.us